VIII Turbo Won't Boost Over 28psi
 

Alittle background info-

Car was on a stock motor with stock VIII turbo/9.8HS, STMTuned @33psi on Stock ECU. No issues whatsoever. Winter comes, I ditch the stock ecu, and 9.8HS and upgrade to AEM/10.5HS among other parts (IC piping, 02 Housing etc). When we throw the car back on the dyno, the most boost AEM was reading was 29psi. That's turned all the way up on my Hallman Pro MBC. We boost leak tested it, and everything was inline. Still wouldn't run anymore boost.
About a month goes by, and I put a few holes in the stock motor, incomes a BR2.0LR, same turbo. We hit the dyno again, same issue...29psi max boost. We tightened the arm on the actuator to see if it helped at all and got no increase, still 29psi turned all the way up. So figuring the turbo was out of breathe, we ran it as is.
Fast forward to this year, motor came out and went to Buschur, got refreshed and is back in. We throw the car on the dyno again, same turbo and now it only will run 28psi, Turned all the way up.
There is almost ZERO shaft play on this turbo, and the Hallman will lower boost if turned down but just gets to that point where the boost barely inches up with turns on the controller. Looking back I see that the boost issue started after the 10.5HS was installed, but there was no cracks in the housing or turbine area whatsoever.

Has anyone had similar issues or potentially any input on this issue?

Have you tried a different WGA? What about swapping on another stock turbo?

The first things that came to my mind were boost leaks, not enough preload on the WGA, maybe a pre turbo exhaust leak...

It sounds like you've already addressed all of these likely culprits. The stock turbo is certainly capable of producing more than 28# as you are aware so something clearly isnt right. Have you visually inspected the flapped on your hotside to make sure it is properly seated?

I've checked it out before, but not in a suspicious way where I would notice the flapper not seating properly. Now that you mention it, Cory Bowers, STM's welder/Tech said that he suspected some type of flapper issue and he's usually on the money with that stuff. I'm going to take the turbo off tonight and thoroughly check it out, I might even throw my 9.8HS back on and have Em check it out on the dyno, at this point I feel like if I can run 33psi on a 9.8HS with this setup it'd make more power than 27psi with the 10.5HS

It's your DV. It's getting blown open. Mine did the same thing. :)

I have the newest version of the TiAL Q, so it's definitely not getting blown open.

Don't assume anything. Block off the DV just for one WOT run and check out this possibility before discarding the idea offhand. Are you on the stock MHI actuator?

Incidentally, what O2 hsg. are you running now?

So, give us some useful and relevant info: Back the knob on your MBC all the way out counterclockwise to the lowest possible boost setting and do a WOT run in 4th gear. Give us the peak boost reading on your boost gauge with the MBC set this way to full soft.

Yes I am on the stock actuator, the 02 housing is a DME 02 (exactly the same as a Megan but the plate tack welded on says DME). I do not have a boost gauge, just an AEM Wideband in the glove box. The only time I touch the boost controller is when it's on the dyno and Emery has the laptop hooked up. If I recall correctly I think the lowest it would go is in the 12-15psi range because when I put it back together we start with the boost all the way down

I'm really leaning towards a Hotside issue, mainly because that's when the issues started. Coincidentally the same time I installed the TiAL, it has a 6psi spring in it but as far as I know the spring pressure is vacuum related and doesn't affect achievable boost

No boost gauge on a semi-built car????


OP, did I meet you at STM 1-2 summers ago?

Yup, no boost gauge. Just a Wideband in the glovebox that I use as needed. I like the clean bone stock interior look, and I don't need to check boost, whatever is tuned to it stays at. I usually boost leak/spark plug check/oil change every 1k-1500mi so I stay on top of things.

Another thing to add-The Throttle body shaft seals are new as well.

I know we tightened the wastegate 1-2 turns tighter and didn't really see an increase in max pressure, Im wondering if when I swapped Hotsides I adjusted the rod out slightly for a better fit and I never had the proper tension in the first place?

I'm pretty sure we chatted for a bit while your Kelfords were getting tossed in right?

Ok, that makes more sense now.

And if you have a boost leak tester, why not try that and see if you can find a boost leak?